Production of pulp of high alpha cellulose content



Patented Aug. 18, 193i r 1,819,002

UNITED v stares. PATENT OFFICE GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE, ASSIGNOB T BROWN COMZPANY,

OF BERLIN, NEW HAMPSHIRE; A CORPORATION OF MAINE PRODUCTION OF PULP 0]? HIGH ALPHA CELLULOSE CONTENT No Drawing. Application filed March 25, 1930. Serial No. 438,905.

Thisinvention relates to the production of high mar ret value. Thus, the extraction fromraw cellulosic material, such as wood, of pentosans from the raw wood with water of pulps which have an alpha cellulose conmakes possible the use of a liquor of comtent much higher than that present in the paratively low alkalinity in the last cooking usual chemical wood pulps, such as sulphite step to complete fiber liberation and yet proor kratt, which accordingly constitute higher duces a product of high alpha cellulose congrade raw material for papermaking and or tent. Again, the process is simple and the conversion into cellulose derivatives than the total time of processing beginning with the usual chemical wood pulps. raw wood chips and ending with the liberated 10 The process of the present invention, which pulp is no longer than the time consumed in is especially applicable to raw cellulosic mathose processes where refined wood pulpsare terial such as wood, comprises three cooking produced by first liberating the fiber by a steps, but the first two cooking steps are not chemical pulping process such as the sulphite designed to effect fiber liberation, but to or so-called kraft process, and then digestcondition the wood so that it may be easily ing the liberated fiber in alkaline liquors, converted into a pulp of the desired charespecially when the raw pulp is such, e. g., acter by the last cooking step. The ,wood kraft pulp, as to require an additional treatemployed as a raw material is cut into chips ment with agents such as chlorine water prior of the usual size employed for chemical pulpto digestion in the alkaline refining liquor.

ing processes before being sub ected to The initial treatment of the wood with super 7 processing in accordance with the present heated water, as previously stated, acts upon invention. The initial step of the present pentosans, but little, if any, ligneous matter process consists in cooking the wood chips at is removed thereby. The ligneous matter is, elevated temperature and under pressure in however, so modified by this treatment that 25 water, under which conditions the water exsubsequent cooking wi h bisulphite liquor 7 tracts from the wood a large proportionof does not readily produce fiber liberation. the pentosans present therein. The wood Accordingly, it is easy to maintain the woo chips are then cooked short of fiber liberachips in the form of chips throughout the tion in a sutiable bisulphite liquor which cooking operation with the bisulphite liquor,

reacts upon and dissolves principally the even though sufiicient ligneous matter is religneous groups present in the wood. The moved therefrom so that after the final cook wood chips are then cooked to complete in -an alkaline liquor to complete fiber liberfiber liberation in an alkaline liquor at eleation, the resulting pulp is of high cellulose vated temperature and under pressure. The content and is whitened by a comparatively 35 resulting product'is characterized by its high light bleaching treatment. Evidently only alpha cellulose content, its low pentosan cona portion of the ligneous matter present in tent, and its easy bleachability to whiteness the wood responds to solution by the action with little loss of alpha cellulose. It is of the bisulphite liquor, whereupon the rest further characterized by a so-called solution of the ligneous matter, which has been modiviscosity much lower than that possessed by fied by the action of the bisulphite liquor,

the usual chemical wood pulps, such low solureadily responds to solution by the action of tion viscosity rendering it more suitable for the alkaline liquor. use in the preparation of cellulose deriva- While various examples of procedure falltives which are to be used as solutions of ing within the purview of the present inven- 45 low viscosity in the production of such prodtion are possible, I shall give for purposes 0 5 ucts as artificial silk, films, and lacquers. illustration only one example, which has been A- process such as the foregoing is advanfound to yield an eminently satisfactory tageous. in that it necessitates the use of a product. Wood chips, e. g.,spruce, are cooke comparatively low amount of expensive in a closed digester in water for two to three chemical in the production of cellulose pulp hours at temperatures of from 250 to 400 F., a temperature of about 325 F. representing one at which the desired extraction of pentosans from the wood proceeds at a satisfactorily rapid rate. The aqueous extracting liquor is then drained from the chips and the chips may, if desired, be washed with fresh water, but washing need not necessarily be practised. The water-extracted chips are then cooked short of fiber liberation in a suitable bisulphide liquor, for instance in a sodium or calcium base bisulphite liquor containing 1% combined and 5% free S0 such a liquor corresponding to the liquors customarily used in the production of sulphite pulp. lVhen cooking is effected at, say, 250 F. for about from two to four hours in such a liquor, the chips remain as such through out the cooking operation, and show ver little evidence of pulping, even though they are somewhat softer than the raw wood. Other types of acid sulphite liquors may be employed, for instance a sulphurous acid solution of sodium sulphate or sodium acid sulphate, in which case the liquor may also contain about 5% free S0 If desired, the bisulphite liquor may be one containing a high combined S0 content in the form of a soluble bisulphite, such as sodium bisulphite, in which case the combined S0 may advantageously be approximately equal to the free 0 content of the liquor. For example, a bisulphite liquor containing approximately 4% free and 4% combined S0 may be employed, in which case the cooking of the chips is preferably effected at about 300 F., in order to promote the desired rate of removal of ligneous matter from the chips. After the cooking operation, the bisulphite liquor is drained from the chips and the chips are preferably washed to remove residual acid liquor and organic matter, so that alkali of the final alkaline cooking liquor will not be consumed in the neutralization of acid or associated organic matter. The washed chips are then cooked in an alkaline liquor of the type used in the so-called soda and kraft processes, but the alkalinity of the liquor may be much lower than the alkalinity of the cooking liquors of those processes wherein the liquors must accomplish reactionupon and solution of much more organic matter from the raw wood than that to be removed from chips which have been previously cooked as herein described. For example, the

washed chips may be cooked to complete -ber liberation in about two to three hours at a temperature of from 300 to 350 F. iIi

a liquor containing only about 1.5 pounds of alkali per cubic foot, calculated as Na O. The alkali is preferably made up of both caustic soda and sodium sulphide, the latter present to the extent of about corresponds to the sulphidity of An alkaline liquor makes possible the alkali being 40%, which a typical kraft liquor. of such a composition production of a product having optimum physical characteristics, includin a tear re sistance comparable to, or even higher than, that possessed by the usual kraft pulp.

if desired, the bisulphite cook may be performed on the raw wood, whereupon the wood so cooked may then be extracted with superheated water, but this sequence of steps is ordinarily less desirable than that hereinbefore described, even though it leads to the product desired, as the active chemical of the bisulphite liquor is consumed in reacting upon and dissolving pentosans which might otherwise be reacted upon and dissolved by water alone. In other words, the process of the present invention ispreferably practised with the water alone serving to extract as much undesirable non-fibrous matter from the wood as possible, so that the valuable chemical used in the subsequent cooking operations may be utilized forreaction upon and solution of only those wood components which are insoluble in superheated water alone.

- I claim:

1. A process which comprises cooking raw cellulosic material short of fiber liberation in superheated water and in an acid sulphite liquor, and then cooking to complete fiber liberation in an alkaline liquor.

2. A process which comprises cooking raw ccllulosic material in superheated water, then cooking short of fiber liberation in an acid sulphite liquor, washing, and cooking to complete fiber liberation in an alkaline liquor.

' 3. A process which comprises cooking wood chips in water at about 250 to 400 F then cooking short of fiber liberation in an acid sulphite liquor, and cooking to complete fiber liberation in an alkaline lfquor of comparatively low alkalinity.

In testimony whereof I haveafiixed my signature.

GEORGE A. RICHTER. 

